The invention relates to generators in general and more particularly to an improved single phase, metal encapsulated generator takeoff for generators of large power rating. Generator takeoffs consisting of a rigid inner conductor and a cylindrical, gas-tight tubular envelope which surrounds the inner conductor concentrically and in which the inner conductor is supported by support insulators, and which has ring-like expansion compensators at suitable spacings for taking up length changes caused by temperature variations, the inner conductor being connected to the brought-out leads of the block transformer by expansion strips, for each phase are commercially available.
The takeoffs of generators of large power ratings to block transformers require a very large amount of space because of the high voltages and large currents that occur. Thus, according to the new design guidelines of the power station operators, a conductor diameter of 760 mm and a tubular enclosure diameter of 1500 mm are required at the block transformer terminal for generator takeoffs with a generator power of 1700 MVA and which are self cooling. The block transformers which correspond to these power requirements and step up the medium voltage supplied to a high voltage of 380/220 kV, are accordingly large.
The cylindrical inner conductor for each phase is surrounded by an outer, hermetically sealed tubular enclosure. Compressed air with an overpressure of about a 200 mm water column over ambient pressure is maintained in the interior of the tubular enclosure, in order to prevent moisture and dust from penetrating into the interior of the tubular enclosure. The inner conductors and the likewise electrically conducting tubular enclosure carry phase shifted currents for each of the three phases in order to keep the short circuit forces between the phase conductors low and to maintain centering of the inner conductor. At suitable spacings, the tubular enclosures have expansion compensators in the form of bellows or corrugated pipes, in order to take up the length changes of the tubular enclosure as the result of variations of the ambient temperature and thereby to reduce the occurrence of mechanical stresses in the axial direction of the takeoff.
Because of the tolerance problems that occur, the connection of the generator takeoff to the block transformer always becomes an extremely difficult and labor consuming undertaking. Thus, when connecting block transformers with an apparent power of 725 MVA, tolerances of about .+-.50 mm in the horizontal and vertical direction can be expected.
One way to equalize the tolerances is to insert adapters of suitable dimensions for the inner conductor and the tubular enclosure in order to bring about an equalization of tolerances in each individual case. However, this requires extensive modification work.
Another method to equalize the relative position deviations when connecting the generator takeoffs to the block transformer is to provide enlarged flanges for the tubular enclosure at the coupling point, in order to ensure a sufficiently large minimum contact area of the adjoining flanges, the areas of which only partly overlap. The flanges to be joined together are then pressed together by clamps applied from the outside, since the holes in the flanges for receiving the connecting bolts do not line up because of the deviations in position and therefore, direct bolting together of the flanges is no longer possible. This, however, presupposes an extremely strong design of the flanges, so that the forces occurring at the joint between the tubular enclosure and the flange can be absorbed without destruction. The enlargement of the flange diameter also bring about space problems since the space required for each individual generator takeoff connection becomes larger. The spacing between the individual phases of the generator takeoff would therefore have to be increased at the transformer terminals. In addition, this kind of tolerance equalization is also very expensive.
Thus, there is a need for a generator takeoff of the type mentioned above which permits tolerance equalization as well as being easy to install at the block transformer without substantially increasing the outside diameter of the tubular enclosure.